Spent kraft boiling lye treatment by coking - in acidic liquid phase and desulphurisation of coke with hydrogen, for rapid treatment

Treatment of spenk kraft boiling lye comprises na) treating the lye with SO2 in an absorption zone to reduce the pH to >=7, pref. 2-5; (b) fluid coking under autogenous pressure, forming coke, gas and an aq. stream; (c) sepg. the coke and the aq. stream; (d) burning the gas to produce SO2; (e) washing the coke with part of the aq. stream and drying with flue gas; (f) passing H2 at 371-1093, pref. 538-816 degrees C over the coke, with H2S formation; and (g) adding lime and the H2S formed to the aq. stream in an absorption zone, to produce new kraft boiling lye. Only 2 hr. treatment with H2 (at 732 degrees C and 1.05kg/cm2) are needed to reduce the S content of the coke from 14 to 2.14% and a total of 92% of the S in the starting material can be recovered as H2S for use in the process.